Magnetoresistive element

ABSTRACT

A magnetoresistive element of an insulating substrate, a first current conducting ferromagnetic metal film strip on said substrate and having a current carrying ability predominantly in one direction, a second current carrying ferromagnetic metal film strip on the substrate having a current carrying ability predominantly in a direction substantially perpendicular to the aforementioned direction, the ends of said strips being connected together, with a current input terminal connected to the opposed ends of the strips and an output terminal connected to the junction between the two strips.

Umted States Patent 11 1 1111 3, Makino et a]. [45] Dec. 23, 1975 MAGNEIORESISTIVE ELEMENT 2.860.061 12/1958 Risk ass/292x [751 Inventors: Yoshimi Mm .Fufisawflsuwmu 338321;??? 311325 23231 212;11111111111111?"'1:

Okamoto, Yokohama; Iwao Kamiya, 3,716,781 2/1973 Almasi et al. 378/32 R Chigasaki, all of Japan Assignee: Sony Corporation, Tokyo, Japan Filed: July 10, 1974 Appl. No.: 487,282

Foreign Application Priority Data July 13, 1973 Japan 48-97655 US. Cl 338/32 R; 324/46; 338/285; 338/287; 338/307; 338/308; 338/325; 338/330; 340/174 EB Int. Cl. 01C 7/16 Field 0! Search 338/32 R, 32 H, 283-285, 338/287, 279-280, 293, 295, 307-309, 325, 330; 323/94 H; 324/45, 46; 252/512-513, 518-519; 340/174 EB References Cited UNITED STATES PATENTS 4/l9l4 Bicknell 338/325 X Primary ExaminerC. L. Albritton Attorney, Agent, or Firm-Hill, Gross, Simpson, Van Santen, Steadman, Chiara & Simpson [57] ABSTRACT A magnetoresistive element of an insulating substrate, a first current conducting ferromagnetic metal film strip on said substrate and having a current carrying ability predominantly in one direction, a second current carrying ferromagnetic metal film strip on the substrate having a current carrying ability predominantly in a direction substantially perpendicular to the aforementioned direction, the ends of said strips being connected together, with a current input terminal connected to the opposed ends of the strips and an output terminal connected to the junction between the two strips.

6 Claims, 8 Drawing Figures U.S. Patent Dec. 23, 1975 Specific Resistance PUZcm) Sheet 1 of 4 3,928,836

0.1 1/. MnO Fig-1 760 e60 960 -94 Measured Temperature US. Patent Dec.23, 1975 Sheet2of4 3,928,836

MnO Content U.S. Patent Dec.23, 1975 Sheet30f4 3,928,836

\ Example1 Resistance after ageing [130 in air (with reference to resistance before ageing) MnO Content US. Patent Dec. 23, 1975 Sheet 4 of4 3,928,836

Fig.6

MAGNETORESISTIVE ELEMENT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to magnetoresistive elements, and more particularly to a magnetoresistive element suitable for detecting the direction of a magnetic field.

2. Description of the Prior Art It is common practice to detect angular positions of a rotor of a brushless electric motor by means of a magnetoelectric transducer in order to control the currents flowing into the stator coil of the brushless motor. The magneto-electric transducer may, for example, be a semiconductor Hall device, a semiconductor magnetoresistive element, a planar Hall element, or a ferromagnetic magnetoresistive element.

The temperature characteristics of a semiconductor transducer are undesirable, since the number and the mobility of the charge carriers vary widely with temperature. A temperature compensating device is accordingly required in the use of such semiconductor transducers. Moreover, the output of the semiconductor transducer varies with the intensity of the magnetic field. Consequently, when the semiconductive transducer is used as a switching element for detecting the direction of the magnetic field, for example, in a brushless motor, additional circuitry must be employed to improve the accuracy and effect a limiting operation. Consequently, the circuits involved for employing semiconductive transducers are expensive.

The ferromagnetic transducer, on the other hand, has a desirable temperature characteristic because the resistivity of the ferromagnetic transducer varies only slightly with temperature. Moreover, since the ferromagnetic transducer can be saturated with a magnetic field, it can effect a self-limiting operation so as to be insensitive to variation of the intensity of the magnetic field. Consequently, the ferromagnetic transducer is more advantageous than a semiconductive transducer for use as a switching element for direction of the magnetic field. However, a planar Hall element has the disadvantage that its output voltage is small and that it requires the use of a high gain amplifier. Moreover, a conventional magnetoresistive element having two terminals has the disadvantage that the unbalanced voltage at no magnetic field is several orders ofmagnitude as high as the output voltage, although the output voltage is considerably high, and that the drift due to variations in temperature must be compensated.

U.S. Pat. No. 3,405,355 to Hebbert discloses a magnetometer employing thin film magnetic films having magnetoresistive properties. The relationship between the resistivity of the material and the angle of rotation of the magnetization in the film is used to measure external magnetic fields. When a biasing field is applied to the magnetoresistive films, fields of high intensity can be measured.

SUMMARY OF THE INVENTION The magnetoresistive element of the present invention has the advantages of the planar Hall element and those of the conventional magnetoresistive element, without the disadvantages mentioned above. The magnetoresistive element of the present invention is capable of generating a large change in output voltage with changes in direction ofa magnetic field. The element of the present invention is capable of readily performing a .substrate having a current carrying ability predominantly in a direction substantially perpendicular to the aforementioned direction, with the ends of the strips being connected together, and a current input terminal connected to the opposed ends of the strips, and an output terminal connected to thejunction between the two strips. The two strips may be located on the same or on opposite surfaces of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view illustrating the principles of operation of a magnetoresistive element according to this invention;

FIG. 2 is the equivalent circuit diagram of FIG. I;

FIG. 3 is a plan view of a magnetoresistive element produced according to one embodiment of the invention;

FIG. 4 is a graph illustrating the relationship between change of output voltage of the magnetoresistive element and the direction of magnetic field applied to the element;

FIG. 5 is a plan view of a magnetoresistive element according to another embodiment of this invention;

FIG. 6 is a bottom plan view of FIG. 5;

FIG. 7 is a cross sectional view taken substantially along the line VII-VII of FIG. 5; and

FIG. 8 is the equivalent circuit diagram showing three magnetoresistive elementsconnected in parallel with each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I, there is shown a magnetoresistive element 1 which comprises a pair of strips A and 8 formed of a ferromagnetic material having a magnetoresistive effect. The longitudinal direction of the strip A is perpendicular to that of strip B. The strips A and B are connected electrically to each other in series. Current supply terminals 2 and 3 are connected to the opposed ends of the strips A and B. An output terminal 4 is connected to the junction between the strips A and B. A power source 5 is connected between the current supply terminals 2 and 3. One current supply terminal 3 is connected to ground potential. Thus, a sensing circuit6 for magnetic fields is obtained.

A magnetic field H sufficient to saturate the strips A and 8 formed of ferromagnetic material, is applied to the strips A and B at an angle 6 to the longitudinal direction of the strip A. Generally, the resistance of a saturated ferromagnetic material is anisotropic. Resistances p, and p, of the strips A and B will be represented b the Vol t-Thomson's formula:

p sin0+ cos'O (I) giioicos'6+"p sinO (2) where p .L is a resistance of the ferromagnetic strip A or B when saturated with a magnetic field perpendicular to the longitudinal direction of the ferromagnetic strip A or B, and pll a resistance of the ferromagnetic strip when saturated with a magnetic field parallel with the longitudinal direction of the ferromagnetic strip A 3 or B.

FIG. 2 shows a circuit equivalent to FIG. I. A voltage V(6) at the output terminal 4 will be represented by MOHMO) where V is the voltage of the power source 5. By substitution of the equations (l) and (2),

A os20 T up +01.)

and the second term a change of the output voltage AV(6).

The second term AV(0) is converted into A W0) I 4p.

-cos 20- V,

where 2 p p|| pi and p is the resistance of the ferromagnetic strip A or B when no magnetic field is applied to the ferromagnetic strip A or B.

The absolute value of the change of the output voltage is maximum at angles 0, 90. l80 and 270. A switching operation can be most suitably effected when two kinds of magnetic fields at the angles 0 and 90 are applied to the ferromagnetic strips A and B, because signs of the changes AV(0) at the angles 0 and 90 are opposite to each other.

As apparent from the equation (5), the change of the output voltage is independent of the intensity of the magnetic field H, while it varies with the direction of the magnetic field H. it is apparent that the intensity of the magnetic field H should be sufficient to saturate the ferromagnetic strips A and 8.

Moreover, as apparent from the equation (5), the magnetoresistance element 1 is required to be formed of ferromagnetic material with a large Ap/p,, for suitable increase of the change of the output voltage.

The following ferromagnetic metals are known for which Ap/p, is more than 2% at room temperature:

Any one of the above ferromagnetic metals can be used as the material of the magnetoresistive element 1 according to this invention. Among the above ferromagnetic metals, Ap/p for Ni-20C0 alloy is at a maximum (6.48%). Compared with a Ni-Fe alloy, the 80Ni-20Co alloy is very acid resistant, inexpensive and solderable. Therefore, the 80Ni-20Co alloy is the practical material most suitable for the magnetoresistive element.

Another factor for the change of the output voltage is the voltage V,, of the power supply 5. it is possible to increase the change of the output voltage with the voltage V,,, as by the selection of a suitable ferromagnetic metal. However, it is not desirable that the voltage of the power supply 5 be increased, since the consumption ofthe power in the magnetoresistive element, increases with the voltage V which generates a large amount of heat. The consumed power W is proportional to the square of the voltage V and inversely proportional to the resistance v, W= 2 p, Accordingly, the change of the output voltage can be increased in such a manner that the resistance p, of the magnetoresistive element 1 is increased concurrently with the voltage V,,.

The resistance p, of the magnetoresistive element 1 can be easily increased by reducing the widths of the strips A and 8. Consequently, the change of the output voltage of the magnetoresistive element I can be made larger than that of the conventional planar Hall element.

Although the resistances pll and pi vary with temperature, Ap and p, are little affected by temperature, since the resistances pll and p i simultaneously vary. Consequently, the change of the output voltage AV(0) is little affected by temperature.

The magnetoresistive element 1 has three terminals. One of the three terminals is connected to the ground as a common terminal, Consequently, any neighboring circuit, for example, a power supply circuit, can be simplified.

Next, one embodiment of the magnetoresistive element 1 will be described with reference to FIG. 3.

By a vacuum evaporation method, a thin film of 80Ni-20Co alloy material is deposited on an insulating base plate 7 such as a glass slide or a photographic dry plate, to a depth of approximately 600 to 1,000 A. Then, the thin film is etched so as to form the ferromagnetic strips A and B in zig-zag or in strips together with the terminals 2, 3 and 4. The ferromagnetic strips A and B comprise a plurality of main current paths 8 and 9, and associated connecting portions 10 and 11, respectively. The main current paths 8 and 9 are substan tially perpendicular to each other. The last path 80 of the main current paths 8 is connected to the first path 9a of the main current paths 9 in series. The connecting point of the last path 8a and the first path 9a is connected to the terminal 4.

By such an arrangement, the whole length, and therefore, the resistance, of the magnetoresistive element 1 can be increased. Moreover, the size ofthe magnetoresistive element 1 can be minimized. Consequently, the consumed power can be reduced and the change of the output voltage can be increased.

Next, characteristics ofthe magnetoresistive element I will be described.

The total resistance 2 p of the magnetoresistive element 1 is 2.5 kilo-ohms at a thickness of 600 A for the ferromagnetic strips A and B, and an output voltage of I60 millivolts is generated for a voltage of 8 volts ofthe power source 5. in this case, the intensity of the saturation magnetic field is more than 50 oersteds and the consumed power is about 26 milliwatts. Thus, the intensity of the magnetic field to operate the magnetoresistive element I can be low, and the consumed power will be small. At the same thickness of the ferromagnetic strips A and B, an output voltage 240 millivolts is generated and the consumed power is about 58 milliwatts, fora voltage of i2 volts for the power source 5.

At a thickness of I000 A for the ferromagnetic strips A and B, the total resistance 2 p of the magnetoresistive clement I is l.4 kilo-ohms, and an output voltage of I80 millivolts is generated for a voltage of 8 volts for the power source 5, where the intensity of the saturation magnetic field is more than 50 oersteds and the consumed power is about 47 millivolts. At the same thickness of the ferromagnetic strips A and B, an output voltage of 270 millivolts is generated and the consumed power is about I03 milliwatts, for the voltage of l2 volts for the power source 5.

FIG. 4 shows the relationship between the change of the output voltage of the magnetoresistive clement I with a flint thickness of I000 A and the direction ofthe magnetic field with an intensity of 3000 oersteds. The ordinate represents the change of the output voltage AV(0) and the abscissa represents the angle 0. The origin of the angle 0 is shifted from the representation of FIG. I by an angle (1r/4)(45). The afore-described equation (5) proved to be true, since the change of the output voltage AV (6) is in the form of a cosine wave. The changes of the output voltage AV(0) were I04 millivolts at the angle 0, 45 millivolts at the angle 45", I03 millivolts at the angle 90, 0 millivolts at the angle I35, I04 millivolts at the angle I80 and 0 millivolts at the angle 225.

Another embodiment of the magnetoresistive element I will be described with reference to FIG. 5 to FIG. 7.

In this embodiment, a single ferromagnetic strip A, and the terminals 2 and 4 are deposited on the upper surface of the insulating base plate 7, while the other ferromagnetic strip B and the terminal 3 are deposited on the lower surface of the insulating base plate 7. As in the one embodiment, the main current paths 8 of the ferromagnetic strip A are perpendicular to the main current paths 9 of the ferromagnetic strip B. Moreover, annular ferromagnetic films 4a and 4b are deposited on the upper surface and the lower surface of the insulating base plate 7, respectively. The annular ferromagnetic films 4a and 4b are connected to each other through an aperture made in the insulating base plate 7 (FIG. 7). A ferromagnetic film is deposited on the surface of the aperture. The annular ferromagnetic film 4a connects the terminal 4 to the last main current path 8a of the ferromagnetic strip A. Therefore, the last main current ath 8a of the ferromagnetic strip A is connected to tiie first main current pat 9a ofthe ferromagnetic strip 8 through the annular ferromagnetic films 40 and 4b.

When the magnetoresistance element I is put in a heterogeneous magnetic field, the embodiment of FIG. 5 to FIG. 7 is more preferable than the one embodiment of FIG. 3, since the embodiment of FIG. 5 to FIG.

7 can sense the direction of the magnetic field in a more limited space than the embodiment of FIG. 3.

FIG. 8 shows a circuit equivalent to three magnetoresistive elements 1 connected in parallel with each other, in which the power source 5 is used in common. in this case, 9 (6) p,,(0) pll p .L 2 p, and p constant. Accordingly, the three magnetoresistive eIe ments I can operate independently of each other. That is one of the advantages of the magnetoresistive element according to this invention.

A plurality of the magnetoresistive elements may be connected in series with each other. Instead of the Ni co alloy, the strips A and B may be formed of 80Ni- 20Fe alloy with a large Ap/p so the strips A and B can be saturated with a magnetic field having a lower intensity.

Moreover, the main current paths of the one ferromagnetic strip may be at an angle other than 90, for example, at to with the main current paths of the other ferromagnetic strip, so long as the characteristic of the magnetoresistive element I is not deteriorated.

Although illustrative embodiments of this invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the novel concepts of this invention, as defined in the appended claims.

We claim as our invention:

I. A magnetoresistive element comprising an insulating substrate, a first current conducting ferromagnetic metal film strip on said substrate and having a current carrying ability predominantly in one direction, a second current carrying ferromagnetic metal film strip on said substrate having a current carrying ability predominantly in a direction substantially perpendicular to said one direction, first ends of said strips being connected together, a current input terminal connected to the opposite ends of said strips and an output terminal connected to the junction between the two strips.

2. The element of claim I, in which both strips are located on the same surface of said substrate.

3. The element of claim I, in which said strips are located on opposite surfaces of said substrate.

4. The element of claim I, in which said first and second strips each include a plurality of parallel strips connected electrically in series.

5. The element of claim I in which each strip is composed of an alloy containing about 80% by weight of nickel and about 20% by weight of iron.

6. A magnetoresistive element comprising an insulating substrate, a first current conducting ferromagnetic metal film strip on said substrate and having a current carrying ability predominantly in one direction, a second current carrying ferromagnetic metal film strip on said substrate having a current carrying ability predominantly in a direction substantially perpendicular to said one direction, first ends of said strips being connected together, a current input terminal connected to the opposite ends of said strips and an output terminal connected to the junction between the two strips. wherein each strip is composed of an alloy containing about 80% by weight of nickel and about 20% by weight of cobalt.

II i t l t Page 1 of 5 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No. 3,928,856 Dated Decgn ber 25. 1975 Inventor(s' Yoshimi Makino 'et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Cancel the sheets of drawings and substitute the attached sheets Column 2, lines 62 and 63, change A (9) sin 9 c0s 9 2 P 9) :fl 9 +4 cos 9 A 2 h (9) eacos 9 sin 9 Y Page 2 of 5 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,928,836

DATED December 23, 1975 INVENTOR(S) Makino et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 64, change to line 66, change j/ to Q Column 4, change the equation at line 20 from line 38, change "45" to --O--,

Patent No. 5,928,836 Page 5 of 5 Patent No. 5 928 856 Page h of 5 ANGLE e-- Patent No; 3,928,856 Page 5 of 5 Signal and Scaled this twenty-second 0f June1976 [SEAL] A nest: 

1. A magnetoresistive element comprising an insulating substrate, a first current conducting ferromagnetic metal film strip on said substrate and having a current carrying ability predominantly in one direction, a second current carrying ferromagnetic metal film strip on said substrate having a current carrying ability predominantly in a direction substantially perpendicular to said one direction, first ends of said strips being connected together, a current input terminal connected to the opposite ends of said strips and an output terminal connected to the junction between the two strips.
 2. The element of claim 1, in which both strips are located on the same surface of said substrate.
 3. The element of claim 1, in which said strips are located on opposite surfaces of said substrate.
 4. The element of claim 1, in which said first and second strips each include a plurality of parallel strips connected electrically in series.
 5. The element of claim 1 in which each strip is composed of an alloy containing about 80% by weight of nickel and about 20% by weight of iron.
 6. A magnetoresistive element comprising an insulating substrate, a first current conducting ferromagnetic metal film strip on said substrate and having a current carrying ability predominantly in one direction, a second current carrying ferromagnetic metal film strip on said substrate having a current carrying ability predominantly in a direction substantially perpendicular to said one direction, first ends of said strips being connected together, a current input terminal connected to the opposite ends of said strips and an output terminal connected to the junction between the two strips, wherein each strip is composed of an alloy containing about 80% by weight of nickel and about 20% by weight of cobalt. 